OBJECTIVES: Injuries and fatalities resulting from drunken driving constitute a major national problem. There is a compelling need to identify more effective approaches to reduce this alcohol related public health threat. On Sept. 17, 1981, the state of Maine enacted what its governor has called "the toughest drunk driving law in the nation." The comprehensive new program intends to deter drunk driving and alcohol related accidents by 1) expediting the detection, arrest and judicial processing of offenders; 2) imposing stiffer penalties which are sufficiently stringent, automatic, and uniform to deter potential offenders but not so severe that they will not be enforced, and 3) increasing penalties for new offenses by previously convicted offenders. There are also provisions for public education about the law and its enforcement. The simultaneous enactment of these legal changes permits us to conduct an unprecedented natural experiment. We will compare, the experience of Maine with that of Massachusetts, a state with drinking and driving laws similar to Maine's previous laws. Fatal and injury accident rates in each state will be compared for five years preceding and three years following the law. Random digit dialing telephone surveys of approximately 1000 persons in each state have been completed prior to the law's enactment and will be repeated twice at yearly intervals. these surveys will prospectively assess whether the new laws have a perceived deterrent effect on frequency of drunken driving which derives from increases in public perceptions in Maine relative to Massachusetts concerning either: 1) likelihood of arrest if a person drives after drinking; 2) likelihood of conviction if arrested or; 3) certainty and deverity of punishment if convicted. Surveys of police and court officials in each state and a monitoring of arrests and judicial processing of arrests will explore whether possible changes in public perceptions of enforcement are influenced by strategies and intensity of enforcement efforts. Our design controls potential confounding variables such as changes in weather, gasoline availability, or miles driven and it explores the effects on drunken driving and accidents of intervening variables such as public perceptions of police and judicial enforcement of the legislation. This study has clear and obvious importance for other states and countries interested in reducing alcohol related fatal and non fatal traffic accidents.